Vehicle electric motor drive system

ABSTRACT

A vehicle is driven by an inductor type synchronous motor coupled to each wheel, a diesel engine on the vehicle, and first and second high frequency rotating generators driven by the diesel engine for providing power to the motors for the front and rear wheels, respectively. An electric drive for each motor include means for deriving a control signal modulated at motor speed, a cycloconverter between the motor and its generator regulated by the control signal, tachometer means for deriving a speed signal which is a function of motor speed, and control means responsive to the speed signal for varying the magnitude and shifting the phase of the control signal as a function of motor speed to maintain the output power from the motor constant over a speed range. The vehicle has a power pedal for controlling vehicle speed and means for deriving a power signal which is proportional to the power pedal setting selected by the vehicle operator. The control means is responsive to both the power signal and the speed signal and the speed and regulates the magnitude and phase of the control signal so that motor output power is constant at the selected power level over the speed range. The synchronous motor has a characteristic for each selected power level whose polar coordinates are the magnitude and phase angle of the terminal voltage to be applied to the motor to keep the motor rotor in synchronism with the rotating stator field over the speed range. The control means includes function generating means responsive to the power and speed signals for deriving first and second signals which are the rectangular coordinates of the characteristic for the selected power level. The control means also includes a rotary inductor, vector adder which constitutes the control signal deriving means and has a pair of displaced energizing windings which receive the first and second signals, an output winding inductively coupled to both energizing windings in which the control signal is induced and which is the vector sum of the first and second signals, and ferromagnetic rotor means connected to the motor rotor for cyclically modulating the flux linkage between the energizing and output windings to generate the control signal as it rotates.

United States Patent [72] Inventors William L. Ringland Greendale; Manfred E. Neumann, New Berlin; Ernst K. Kaeser. West Allis; Thomas P. Gilmore, Wauwatosa; Allois F. Geierbach, Milwaukee, all of, Wis.

[21] Appl. No. 824,223 [22] Filed May 13, 1969 [45] Patented June 8, 1971 [73] Assignee Allis-Chalmers Manufacturing Company Milwaukee, Wis.

[54] VEHICLE ELECTRIC MOTOR DRIVE SYSTEM 96 Claims, 40 Drawing Figs.

[52] U.S.Cl 318/171, 318/176, 318/227, 318/231 [51] Int. Cl 1102p 1/52 [50] Field ofSearch 318/231, 171, 176, 189, 227

[56] References Cited UNITED STATES PATENTS 3,394,297 7/1968 Risberg 318/231 3,164,760 l/1965 King 318/231 3,402,333 9/1968 Hayner et al. 318/171 3,443,184 5/1969 Lemmrich 318/231 FOREIGN PATENTS 745,840 3/1956 Great Britain 318/231 Primary ExaminerOris L. Rader Assistant ExaminerK. L. Crosson Attorneys- Lee H. Kaiser, Robert B. Benson and Thomas F.

Kirby ABSTRACT: A vehicle is driven by an inductor type synchronous motor coupled to each wheel, a diesel engine on the vehicle, and first and second high frequency rotating generators driven by the diesel engine for providing power to the motors for the front and rear wheels, respectively. An electric drive for each motorinclude means for deriving a control signal modulated at motor speed, a cycloconverter between the motor and its generator regulated by the control signal, tachometermeans for deriving a speed signal which is a function of motor speed, and control means responsive to the speed signal for varying the magnitude and shifting the phase of the control signal as a function of motor speed to maintain the output power from the motor constant over a speed range. The vehicle has a power pedal for controlling vehicle speed and means for deriving a power signal which is proportional to the power pedal setting selected by the vehicle operator. The control means is responsive to both the power signal and the speed signal and the speed and regulates the magnitude and I phase of the control signal so that motor output power is constant at the selected power level over the speed range; The synchronous motor has a characteristic for each selected power level whose polar coordinates are the magnitude and phase angle of the terminal voltage to be applied to the motor to keep the motor rotor in synchronism with the rotating stator field over the speed range. The control means includes function generating means responsive to the power and speed signals for deriving first and second signals which are the rectangular coordinates of the characteristic for the selected power level. The control means also includes a rotary inductor, vector adder which constitutes the control signal deriving means and has a pair of displaced energizing windings which receive the first and second signals, an output winding inductively coupled to both energizing windings in which the control signal is induced and which is the vector sum of the first and second signals, and ferromagnetic rotor means connected to the motor rotor for cyclically modulating the flux linkage between the energizing and output windings to generate the control signal as it rotates.

PATENTEU Jun awn sum 0311f PATENTEU JUN 8 mm SHEU 05 0F SHEET 09 0F usmkkvb y Wm PATIENT-ED JUN 8197i v vQM PATENIED, JUN 8197i sum '10 0F gig-45d PATENTED JUN 8 I971 sum 13 0F VEHICLE ELECTRIC MOTOR DRIVE SYSTEM This invention relates to a synchronous electric. motor drive system and in particular to such a synchronous motor system having selectively variable power output levels and providing substantially constant output power over a wide speed range for each power level and which finds particular utility in an electrically driven vehicle.

Electrically driven vehicles may employ a diesel, gasoline, or turbine engine as the primary source of power, or prime mover. The prime mover may drive one or more generators which, in turn, power one or more electric motors connected to the wheels or tracks of the vehicle. On wheeled vehicles it is often advantageous to utilize a separate motor for each wheel. An electric control may be interposed between the enginedriven generators and the motors of such a vehicle to regulate the application of electrical power to the motors and wheels.

In the past most electrically driven vehicles have utilized direct current electrical apparatus. Direct current motors, particularly those of the series types, are readily adaptable to electric drive systems because of their ease of control, and further the electrical controls for direct current motors and generators are simple and well developed. However, the commutators and rotating armature coils required by direct current machines add to their manufacturing and maintenance cost.

Electrically driven vehicles are known which employ alternating current motors that are simple and reliable in construction. However, since the speed of an alternating current motor is determined by the frequency of the alternating current source, a control must be provided to convert the fixed frequency of the source to the required motor frequency which varies with speed.

The simplest type'of alternating current motor is the induction motor, but the differential, or slip, between the speed of the rotor and that of the rotating stator field presents difficulties in using a frequency detector driven by the motor shaft for controlling the frequency converter which supplies the variable frequency to the motor stator. The stator frequency must be higher than the detected rotor frequency by the amount of the slip frequency, and further the slip results in heat losses in the rotor which are difficult to remove, particularly at low speeds. The torque of an induction motor is proportional to the square of the voltageto-frequency ratio applied to the stator winding. For constant power and constant r.p.m. slip conditions, the voltage applied to an induction motor over a desired speed range must increase as the square root of the applied frequency. ln a typical instance of l6 to 1 frequency (and motor speed) range at constant power, the maximum supplied voltage required is four times the minimum voltage. Inasmuch as the size of the power supply in a drive system, including the generator and power controlling elements, is determined by the maximum voltage required as well as the maximum current required, a large power supply is necessary for an electric drive system using induction motors.

Because the speed of a synchronous motor is inherently proportional to applied frequency, synchronous motors have generally been employed in constant speed drive systems where the motor is energized from a constant frequency source such as a 60 cycle per second power line. When energized at this frequency, the torque of a synchronous motor assumes a level sufficient to cause the motor to drive the load in synchronism with the rotating. stator field. Such conventional synchronous motor operation is one of constant speed, variable power due to the variable motor torque.

It is an object of the invention to provide an electric drive system capable of operating over a wide speed range at constant motor voltage, current, and power.

It is another object of the invention to provide an electric drive system having selectively variable power output levels and which provides substantially constant output power over a wide speed range for each selected power level.

lt is another object of the invention to provide an electric drive system utilizing electric motors of the synchronous type which are easily controlled to produce torque directly proportional to the voltage-totrequency ratio applied to the stator winding,

It is a further object of the invention to provide an electric drive system utilizing electric motors of the synchronous type which are readily controlled to provide constant power over a wide speed range without increasing the applied voltage, thereby permitting use of a small power supply.

It is another object of the invention to provide an electric drive system utilizing synchronous motors wherein motor speed is always directly proportional to the frequency of the applied voltage and thus frequency detecting means driven by the motor can be efficiently utilized to control the frequency converter which supplies variable frequency power to the motor.

It is still another object to provide an electric drive utilizing alternating current electric motors of the type which provide better power factor and efficiency than induction motors.

It is a still further object of the invention to provide a vehicle electric drive that utilizes a synchronous motor having no armature coils and which is therefore capable of rotation at higher peripheral speeds and is simpler to cool than other types of alternating current motors.

A still further object of the invention is to provide a variable frequency electric drive system which utilizes a frequency changer that permits bidirectional power flow to provide regenerative braking.

It is a further object of the invention to provide an electric drive system incorporating a synchronous motor which is particularly suitable for use as a propulsion means for an electrically driven vehicle.

Another object of the invention is to provide a variable frequency electric drive system utilizing a synchronous motor which permits use of a generator and a frequency changer having a voltage rating substantially lower than that of known electric drive systems of equal horsepower.

A further object of the invention is to provide a vehicle electric drive system which transmits the maximum available power of the prime mover to the tractive elements at all vehicle speeds.

Another object is to provide such a vehicle electric drive system wherein, under constant power from the prime mover, maximum torque is provided to the vehicle under starting or low speed conditions.

It is a still further object of the invention to provide a vehicle electric drive system which has the following advantages over mechanical systems which transmit power from the prime mover to the wheels by clutches, shafts, gears, and transmissions:

a. infinitely variable control of speed and power;

b. operation of the vehicle prime mover at constant Speed for maximum available power regardless of vehicle speed;

c. adaptability to.- automatic controls and protective features; greater operating efficiency and reliability;

. ease of maintenance and repair;

. adaptability to different types of prime movers and vehicles;

g. location of powered wheels and the prime mover not restricted by the mechanical transmission elements, thereby permitting readyand effective use of the electric drive system of the invention in articulated and tandem vehicles;

h. power applied to the tractive elements of the vehicle may be individually selected and controlled, thereby permitting steering by controlling the power and speed of the tractive elements on either side of the vehicle;

. electric braking may be provided to the vehicle, thereby reducing the wear, maintenance, and required capability of the mechanical brakes.

These and other objects and advantages of the invention will be more readily apparent from the followed detailed description when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic diagram in block form of the electric drive system of the invention incorporated in a vehicle;

FIG. 2 is a sectional view through a vehicle wheel and the electric motor which drives it in the embodiment of FIG. 1;

FIG. 3 is an exploded perspective view of the electric motor and the angle sensor driven by it in the embodiment of FIGS. 1 and 2, the motor stator and windings being shown as encapsulated in resin;

FIG. 4 is a partial front view showing the rotor and stator of the angle sensor;

FIG. 5 is a graph plotting relative torque provided by the electric drive system of the invention versus relative speed;

FIG. 6 is a graph showing the no-load saturation curve and the rated armature current, zero power factor saturation curve for the electric motor of the embodiment of FIGS. l-S;

FIG. 7a shows the simplified equivalent circuit of the electric motor; FIG. 7b shows its vector diagram for motor operation; and, FIG. 7c shows its vector diagram for generator operation;

FIG. 8 is a graph plotting motor terminal voltage and displacement angle versus speed required to provide maximum rated power over the speed range;

FIG. 9 is a development of the angle sensor stator and rotor and also schematically illustrates the instantaneous voltages generated in the angle sensor secondary windings;

FIGS. I00 and 10b are schematic diagrams illustrating vector addition of the two input signals to the angle sensor prima; ry windings to derive the output signal which controls the cycloconverter;

FIG. 11 is a graph plotting the motor and angle sensor voltages versus motor speed required to obtain constant 50 percent and I00 percent maximum power over the speed range;

FIG. 12 is a schematic diagram in block form of the angle sensor control, the discriminator, and the clipping circuit;

FIG. 13 is a schematic circuit diagram of the function generators of the angle sensor control;

FIG. 14 is a schematic circuit diagram of the cycloconverter and filter and showing the firing circuit in block form;

FIGS. 15:: through 15h schematically illustrate voltages in the cycloconverter of the electric drive system of the inventron;

FIG. 16 is a schematic circuit diagram of the tachometer;

FIG. 17a is a schematic circuit diagram, partially in block form, of the firing circuit for the controlled rectifiers of the cycloconverter; and FIGS. 17b through I7j show signals at various points within the firing circuit of FIG. 17a;

FIG. 18 is a simplified schematic diagram of the relay logic circuit and the motor control;

FIG. 19 is a graph plotting the output voltage VR from current control amplifier versus motor speed;

FIG. 20 is a graph plotting motor field current versus power pedal positions to provide constant power over the speed range for a selected power level; and

FIG. 2] shows curves plotting as polar coordinates the variation of motor terminal voltage VT and displacement angle DT with motor speed illustrated in FIG. 8.

GENERAL DESCRIPTION Referring to FIG. I, an electric drive system 10 in accordance with the invention propels a vehicle (not shown) by providing motive power to the right front, left front, right rear and left rear wheels 12, I4, 16 and I8 respectively. A prime mover on the.vehicle is preferably a hydrocarbon-fueled engine such as a gas turbine or a diesel engine 20 which operates at substantially constant speed, as determined by the setting of its governor, and is capable of providing constant power input to electric drive system 10 under all conditions of vehicle operation.

Electric drive system 10 preferably includes four electric controls, or drives 22, 24, 26 and 28 (shown in block form) for the wheels I2, 14, 16 and 18 respectively. All four drives are substantially identical, and only drive 22 for right front wheel 12 will be described.

Prime mover 20 drives a first generator 30 which provides electrical power for electric drives 22 and 24 that operate front wheels 12 and 14 and also drives a second generator 32 which provides electrical power for electric drives 26 and 28 which operate the vehicle rear wheels 16 and 18. Generators 30 and 32 are similar and may be conventional high frequency polyphase alternators, and only generator 30 will be described. Generator 30 preferably has a stationary exciting coil 34 energized from a suitable power supply (not shown) and three Wye-connected armature windings 36A, 36B and 36C which generate three-phase alternating current voltages A, B and C in high frequency, constant power buses 38A, 38B and 38C respectively. Prime mover 20 runs at nearly constant speed so that the input power to electric drive system 10 and the frequency of the alternating current generated by generators 30 and 32 are nearly constant.

The input signals to electric drives 22, 24, 26 and 28 which control the transmission of power from generators 30 and 32 to vehicle wheels 12, I4, 16 and 18 are preferably derived from conventional driver-operated vehicle controlling apparatus including a steering wheel 40, a travel direction and speed limit selector 42, a power pedal 44, and a brake pedal 46 which are coupled through a master driver-operated control circuit 48 to electric drives 22, 24, 26 and 28.

Electric drive 22 includes a synchronous motor 50 which preferably is of the inductor type and has a rotor 52 mechanically coupled to right front wheel 12 through appropriate gearing (shown in FIG. 2), a three-phase armature winding, or stator winding 54, and a field winding 56 mounted on the motor stator. Electric drive 22 converts the constant frequency, constant voltage output of high frequency generator 30 to a variable frequency, variable voltage, variable phase alternating current for application to armature winding 54 to regulate the torque and speed of synchronous motor 50.

Electric drive system 10 transmits the constant power output of prime mover 20 to the vehicle wheels 12, 14, 16 and 18 over a wide range of speed. The hyperbolic torque versus speed characteristic of electric drive system 10 to accomplish such transmission of constant power from prime mover 20 to the vehicle wheels over a speed range of 15 to I is shown in FIG. 5. Torque and speed are conveniently related for purpose of description to base values taken at the minimum speed at which constant maximum power is transmitted. The base rating of electric drive system 10 wherein relative torque is arbitrarily designated 1.0 and relative speed designated I.0 is shown in FIG. 5 wherein the full line curve corresponds to the maximum power capability of diesel engine 20 with power pedal 44 fully depressed and with total power equally divided between the individual wheel drives 22, 24, 26 and 28. However, drive system 10 includes means described hereinafter to reduce motor torque under operating conditions requiring less than rated power as represented by the dotted line curve designated reduced power" in FIG. 5. Vehicle speed, motor speed, and motor frequency are all directly proportional because of the use of synchronous motors 50 and the fixed ratio gearing between motors 50 and wheels l2, l4, l6 and 18. Further, motor torque and vehicle tractive effort are also directly proportional because of such fixed ratio gearing.

In the preferred embodiment of the invention motor 50 is of the synchronous inductor type, although any type synchronous motor having adjustable field excitation, including the conventional salient pole type, may be used in electric drive system I0. The conventional saturation curves of synchronous motors are commonly used to show the relationship between stator terminal voltage VT and field current I, for various load conditions. Since synchronous motors are usually operated at constant speed corresponding to a terminal voltage having a fixed frequency of 60 cycles per second, such saturation curves are usually shown for a fixed frequency. The effect of armature resistance on these synchronous motor characteristics is usually small but becomes increasingly significant as the frequency approaches zero.

When synchronous motor 50 is operated at variable frequency, as in electric drive system 10, more meaningful saturation curves which illustrate the effects of frequency variation and armature resistance at low speeds can be derived by replacing the terminal voltage VT the variable (VT +-T,,R,,)/F as illus trated in FI GF6 which shows the no-load saturation curve and the rated armature current. zero power factor saturation curve for a typical synchronous motor 50 suitable for electric drive system 10 and where:

VT is the motor terminal voltage:

l is the armature current:

R is the effective armature resistance; and

F is the frequency.

It will be noted that the values shown in FIG. 6 are expressed as per unit quantities relative to the base rating of the motor.

The vector quantity VT +l R is an internal voltage, commonly called the voltage behind the resistance, and represents the vector sum of the terminal voltage and the armature resistance drop, observing the appropriate phase angle between the two vectors. Commonly used convention considers'the power component of armature current to be positive for generator operation negative for motor operation. Therefore, for motor operation the vector VT +T,,R,, is less than VT for power factors in the normal operating range near unity where VT and I, are displz ed approximately 180 (see FIG.'7b). The total quantity (VT +T,,R,,)/F is proportional to the net magnetic flux linking the armature winding of motor 50, which net magnetic flux is the resultant of that generated by the armature winding 54 and field winding 56.

The saturation curves of FIG. 6 permit close approximation, by well-known methods, of the field current I, corresponding to any load condition. In the preferred embodiment of the invention, electric drive 22 holds the field current l inmotor 50 constant for a desired armature current corresponding to a given position of power pedal 44. As motor speed and frequency increase above the base value F=l.0, the electric drive 22 of the preferred embodiment also holds theterminal voltage VT constant for a given power pedal position, thereby resulting in the net magnetic flux, as represented by variable (VT l,,)/F decreasing very nearly inversely proportional to frequency F. These conditions are represented in FIG. 6 for rated armature current by the vertical line at I,=2.5 designated constant I, for I,,=l.0," and it will be noted that the variable (VT +T,,R,,)/F decreases from a value of 1.0 at frequency F 1.0 along this constant field current line to a value of 0.5 at frequency F=2.0 and then decrease further to a value of 0.2 at F=5. Below frequency F=l.0, the terminal voltage VT is reduced by electric drive 22 as described hereinafter but at a rate that results in the net fluxing rising to a maximum as the frequency approaches zero. With the field current I, and terminal voltage VT constant, the armature current 1,, is close to rated value (I ,1 .0) and the power factor close to unity over the entire range of frequency, thereby resulting in the electric drive system 10 having the hyperbolic constant power speedtorque characteristic shown in FIG. 5. Assuming that electric drive system 10 is designed to have a power rating matching that of diesel engine 20, this speed-torque curve of FIG. 5 might alternatively be designated maximum electric drive system continuous capability. When less than rated power is required to drive the load and power pedal 44 is not fully depressed, the speed-torque characteristic may be represented by the dotted line curve designated reduced power in FIG.5.

Electric drive 22 regulates the terminal voltage VT applied to armature winding 54 of electric motor 50 as described above and also shifts the applied terminal voltage VT through the required phase angle relative to the angular position of the rotor to obtain the constant power torque-speed characteristic shown in FIG. 5. Such required phase angle is best described by reference to FIG. 7a, which shows the simplified equivalent circuit of synchronous motor 50 under steady state conditions, and to FIGS. 7b and 7c which show its vector diagram for motor and generator operation respectively and wherein:

E is the internal voltage proportional to the field current;

X, is the effective synchronous reactance for all field positions relative to the armature m.m.f.; and

R is the effective armature resistance.

The armature current I. results from the vector voltage difference acting on the machir t impedance, and thus:

D= +L (R.+X. FIG..7b illustrates the vector diagram of this relationship for motor operation approximating the conditions in electric drive 22 at rated load for speed F =1.0, and FIG. 70 illustrates the vector diagram for generator operation approximating the conditions in electric drive 22 at speed F=1.0, with braking power less than rated load. The displacement angle DT is the phase angle between the internal voltage E and the terminal voltage VT applied to stator winding 54.

Electric drive 22 advances the terminal voltage VT in phase by the angle (+)DT relative to the physical axis of the internal voltage E on the rotor in order to produce the conditions for motor operation illustrated in FIG. 7b, and it delays the terminal voltage in phase by the angle ()DT relative to the physical axis of E, in order to provide the conditions for generator action shown in FIG. 70.

In the equivalent circuit and vector diagram of FIG. 7, the internal voltage E and effective synchronous reactance X, are proportional to frequency and are multiplied by F for operation at other than base frequency F =1.0.

FIG. 8 illustrates the terminal voltage VT and displacement angle DT which electric drive 22 applies to stator winding 54 of synchronous motor 50 at rated load to provide the desired constant power speed-torque characteristic of FIG. 5 with constant field current, essentially constant armature current and power factor close to unity. It will be noted that the dis placement angle DT is 0 at F=0.0 and approaches at high frequency and motor speed. FIG. 8 shows only two VT curves designated rated power and reduced power, but it will be appreciated that a different VT curve exists for each position of power pedal 44 and the corresponding power output level from motor 50.

Electric drive 22 includes a frequency changer, or cycloconverter 58 which is supplied with constant voltage, high frequency power from generator 30 over buses 38 and is responsive to gating signals from a firing circuit 60 to convert this high and constant frequency power to a lower variable frequency terminal voltage VT supplied over conductors 62 to stator phase windings 54X, 54Y and 54Z of synchronous motor 50. Cycloconverter 58 is shown in detail in FIG. 14 and preferably includes a positive group of three thyristors, or silicon controlled rectifiers associated with each of the three motor stator phase windings 54X, 54Y and 54Z to carry positive current from the three-phase power busses 38A, 38B and 38C and a negative group of three silicon controlled rectifiers associated with each of these three motor stator phase windings to carry negative current from the busses 38A, 38B and 38C.

Firing circuit 60 derives gating signals which cyclically fire the silicon controlled rectifiers in cycloconverter 58 at desired points in the cycles of the high frequency, constant magnitude voltages A, B and C in busses 38A, 38B and 38C to generate the three-phase voltages in conductors L1, L2 and L3 which are applied to stator phase windings 54X, 54Y and 54Z.

Electric drive 22 includes a rotary inductor, vector adder, or resolver, termed angle sensor" 64 driven by motor 50 for deriving a control signal for cycloconverter 58 which is, a.

replica in magnitude, frequency and phase of the voltage VT (shown in FIG. 8) to be applied to stator winding 54 to obtain constant power over the speed range. In order to keep the poles generated in motor rotor 52 locked in with the revolving poles generated by motor stator winding 54, the frequency of the terminal voltage VT applied to stator winding 51 must at all times be in synchronism with rotor speed, and further the terminal voltage must be advanced in phase at all motor speeds by the displacement angle DT between the magnetic flux produced by the field current acting alone and the magnetic flux corresponding to the terminal voltage. Further, the magnitude of the terminal voltage VT impressed on stator winding 54 must be controlled as a function of motor speed in the manner shown in FIG. 8.

The variation in magnitude VT and phase angle DT of the terminal voltage shown in FIG. 8 to be applied to stator winding 54 can be expressed graphically by the loci of an equation in which motor speed is the variable parameter and the mag nitude VT and phase angle DT are the radius vector and vectorial polar coordinates of the curve formed by the loci. FIG. 21 shows such a curve in dotted lines designated rated power" plotting the loci of terminal voltage VT and phase angle DT when motor 50 is delivering rated power and also shows a curve in full lines designated reduced power." The magnitude of the terminal voltage VT to be applied to stator winding 54 as a function of motor speed is the radius vector of such curve, two such vectors VT] and VT2 for the reduced power curve being shown in FIG. 21. The displacement angle by which the terminal voltage is to be advanced in phase relative to the rotor poles as a function of motor speed is the vectorial angle of the curve, two vectorial angles DTl and DT2 for the reduced power curve being shown. It will be noted that the magnitude of the terminal voltage VT is maintained constant from the base speed F =l.0 at the lower limit of the speed range (shown by vector VTl having phase angle DTl) with increase in motor speed, while the displacement angle increases from approximately 40 at F =l.0 to approximately 90 at speed F=3.5, at which the terminal voltage is shown by the radius vector VT2 and the displacement angle by the vectorial angle DT2.

A plurality of different curves can be plotted in FIG. 21 all of which are of the same shape and each of which represents a different position of power pedal 44 and a corresponding different power output level from motor 50. Each curve shown in FIG. 21 can also be defined by its rectangular coordinates x and y which vary as a function motor speed F, or by the parametric equations of the curve having motor speed F as the variable parameter. Electric drive 22 includes an angle sensor control 76 which generates a pair of sine" and cosine" signals V, and V representative of the y and x rectangular coordinates of a curve of FIG. 21 for each position of power pedal 44, and angle sensor 64 vectorially adds such signals and derives an output signal for controlling cycloconvertcr 58 whose magnitude and phase are in accordance with the radius vector and vectorial angle polar coordinates of such curve. Inasmuch as a curve of FIG. 21 is the loci of an equation which expresses the desired variation in magnitude VT and phase angle DT with motor speed as shown in FIG. 8, the terminal voltage VT applied by cycloconvertcr 58 to motor stator winding 54 is in accordance with one of the curves of FIG. 8 corresponding to a given power pedal position. As explained in detail hereinafter, the output signals from angle sensor 64 regulate firing circuit 60 which derives the gating signals for firing the thyristors ofcycloconverter 58.

Rotary inductor, vector adder, or angle sensor 64 in effect converts the signals V, and V representative of the y and x rectangular coordinates of a curve of FIG. 21 into the polar coordinates of such curve. Angle sensor 64 has a secondary winding 66 comprising three Wye-connected secondary phase windings 66X, 66Y and 662 displaced 120 (electrical) and a pair of energizing, or primary windings, termed sine winding 68 and cosine winding 70, displaced 90 electrically from each other magnetically coupled with secondary winding 66. The primary windings 68 and 70 and the three-phase secondary windings 66X, 66Y and 662 are wound on an angle sensor stator 72 (see FIGS. 2, 3 and 4) mounted on the housing of motor 50, and the magnetic flux linkage between the secondary winding 66 and the primary windings 68 and 70 depends on the airgap between the stator 72 and a ferromagnetic rotor 74 connected to the motor rotor 52. The angle sensor rotor 74 is contoured to produce an approximately sinusoidal variation in the airgap and in the flux linkage between each secondary phase winding 66X, 66Y and 662 and the primary windings 68 and 70 as it rotates.

The sine and cosine primary windings 68 and 70 are separately excited with high frequency, in-phase sine and cosine signals V, and V, from angle sensor control 76 which are in accordance with the y and x rectangular coordinates respectively of a curve of FIG. 21 corresponding to a given position of power pedal 44. If motor 50 is at standstill and the angle sensor control 76 were to energize the sine and cosine windings with fixed magnitude, in-phase, high frequency alternating signals, the 90 displaced sine and cosine windings 68 and 70 would have constant ampere turns and induce fixed magnitude, high frequency signals in the three-phase secondary windings 66X, 66Y and 662. The permeances of the paths for the magnetic flux generated by the sine and cosine windings 68 and 70 and the voltage level of the fixed amplitude signals induced in the three-phase secondary windings is a function of the position of angle sensor rotor 74. When motor 50 rotates, the high frequency angle sensor output voltages induced in secondary windings 66X, 66Y and 66Z are no longer fixed in amplitude but rather have a sinusoidal modulation at a relatively low frequency which is representative of the speed of the motor 50. The envelopes of the three angle sensor output signals inducted in the secondary phase windings 66X, 66Y and 662 are displaced l20 (electrical) because of the physical location of these windings on the angle sensor stator 72.

The term output voltage" is used herein to connote either the carrier frequency signals induced in secondary phase windings 66X, 66Y and 662, their low frequency sinusoidal modulation envelopes, or the signals derived therefrom by demodulation to remove the carrier frequency and alternate half waves. The carrier frequency signals induced in secondary phase windings 66X, 66Y and 66Z are designated vi, and their low frequency modulation envelopes and the signals derived therefrom by demodulation are designated VT,. Further, all three such forms of output voltage are directly proportional in magnitude, and their magnitude is represented in curves by the designation VT,.

Angle sensor control 76 receives a reference power signal from protection and regulation circuit 78 (see FIG. 1) which is a function of the position of power pedal 44 and independently controls the signals V and V to sine and cosine windings 68 and 70 of angle sensor 64 as a function of this power signal, thereby controlling the ampere turns of these windings and the magnitude of the signals vt, (and their modulation envelopes VT,) induced in secondary phase windings 66X, 66Y and 66Z which, after demodulation, control cycloconvertcr 58. Thus angle sensor control 76 suitably regulates the magnitude of the signals V, and V to the sine and cosine windings 68 and 70 of the angle sensor 64 to control the magnitude of terminal voltage VT applied to the motor stator winding 54 as a function of power pedal position. Change in position of power pedal 44 varies the magnitude of the power signal and thus changes the length of the radius vector VT in FIG. 21.

Angle sensor control 76 also receives a speed signal from tachometer 80 (see FIG. 1) which is a function of the speed of the motor 50 and modifies the signals V, and V, to the sine and cosine windings 68 and 70 in response to the speed signal in accordance with the y and x rectangular coordinates of a curve of FIG. 21 so that the angle sensor output voltages VT, induced in secondary windings 66X, 66Y and 662 vary linearly (see FIGS. 8 and 11) from zero at zero speed to full value (corresponding to a given position of power pedal 44) at base frequency F=l .0 and remain at full value from F=l.0 to maximum motor speed F=l5.0. Above base speed F=l.0,

angle sensor control 76 unequally varies the magnitude of the signals V, and V, to the sine and cosine windings 68 and 70 in opposite directions as a function of motor speed (see FIG. 11) while maintaining the magnitude of the angle sensor output voltage VT, constant for a given power pedal position, thereby unequally varying the ampere turns and the intensity of the magnetic flux which these windings 68 and 70 generate and shifting the phase of the modulation envelopes VT, of the angle sensor output voltages induced in secondary windings 66X, 66Y and 662 relative to the angular position of the angle sensor rotor 74 while maintaining the magnitude of these voltages constant. The output signals VT, from angle sensor secondary winding 66 control cycloconverter 58, and angle sensor control 76 thus regulates the displacement angle DT of the voltage VT applied to motor stator winding 54 relative to the magnetic poles on motor rotor 52 as a function of motor speed, while maintaining the magnitude of the terminal volt age VT constant for a given position of power pedal 44, by independently varying the magnitude of the sine and cosine signals V, and V, to sine and cosine windings 68 and 70 to obtain the terminal voltage versus speed and displacement angle versus speed characteristics designated VT and DT in FIG. 8.

The three-phase high frequency output voltages vt, from angle sensor secondary windings 66X, 66Y and 662 are demodulated in a discriminator 82 to remove the carrier signal. Discriminator 82 provides three-phase output voltages VT, of motor frequency controlled in magnitude and phase angle relative to a reference axis or the motor rotor, i.e., the axis of internal motor voltage E shown in the vector diagram of FIG. 7b.

The peak voltages of the low frequency output signals VT, from discriminator 82 are limited in a clipping circuit 84 which derives flat-topped output signals VT, (See FIG. 12) when the voltages from discriminator 82 exceed the clipping level.

In order to condition the generator high frequency, constant magnitude voltages A, B and C in the busses 38A, 38B and 38C for generating the synchronizing," or sequence" signals required by firing circuit 60, a filter 86 (see FIG. 1) removes the commutation notches and high frequency noise from the generator voltages A, B and C and regulates the voltage level thereof to derive reference" voltages which are reproductions of the fundamental waves of these generator voltages. Firing circuit 60 combines these three-phase, high frequency output reference" signals from filter 86 with the three-phase low frequency control signals VT, from clipping circuit 84 (which are proportional to the angle sensor output voltages VT,) to derive the sequence" signals A+VT,, B+VT, and C+VT, shown in FIG. Ie, and the firing circuit 60 includes level detectors (described hereinafter) which sense the zero crossing points of such sequence signals and generate the gating signals for the controlled rectifiers of the cycloconverter 58. i

As explained hereinbefore, the terminal voltages VT applied to stator winding 54 and displacement angles DT shown in FIG. 8 will result in the desired speed-torque characteristic of FIG. 5 with constant field current, essentially constant armature current, and power factor close to unity. Voltage drops occur in generator 30 because of the commutating inductance, and additional resistance and reactance voltage drops occur in the controlled rectifiers and center tapped reactors of cycloconverter 58, and the effect of such voltage drops on motor terminal voltage VT and on the controlling input signal voltage to cycloconverter 58 is approximately the same as that of an added resistance in series with the motor. The output voltage VT from cycloconverter 58 to motor stator winding 54 is proportional to, and a replica of, the angle sensor output voltage which controls cycloconverter 58 and would have the magnitude versus speed response of the VT curve in FIG. 8 if such voltage drops and the limiting of the peak voltages in clipping circuit 84 were not taken into consideration. In order to compensate for such voltage drops under load and also for the clipping of the VT, signals in clipping circuit 84, angle sensor control 76 increases the magnitude of the output signal from angle sensor 64 for rated load from a signal having the magnitudeof the full line VT curve to that shown by the curve designated VT, and also varies the phase angle of the angle sensor output signal (which controls cycloconverter 58) in accordance with the curve designated DT, in FIG. 8 rather than along a characteristic similar in shape to the DT curve.

The position of power pedal 44, brake pedal 46 and travel direction selector 42 determine the magnitude of a DC reference power" signal from master driver-operated control 48 which is supplied to the protection and regulation circuit 78 wherein its magnitude may be modified by input signals from a relay logic circuit 88, current transformers which derive signals proportional to the currents in high frequency, constant voltage busses 38, and other means not shown in FIG. I to compensate for direction of vehicle motion, driving or braking of the vehicle, turn compensation, engine stalling or overspeeding, and overcurrent compensation as described in detail hereinafter. An exciting coil, or field winding control 92 regulates the excitation of field coil 56 of motor 50 as a function of the power signal from protection and regulation circuit 78. As described hereinbefore, angle sensor control 76 is responsive to the power reference signal from protection and regulation circuit 78 and to the speed signal from tachometer 80 and derives in-phase alternating signals V, and V to the primary sine and cosine windings 68 and 70 required to produce the motor voltage VT and displacement angle DT shown in FIG. 8 at rated load as a function of motor speed. The constant power, torque-speed characteristic shown in FIG. 5 is obtained when the power pedal 44 is fully depressed and the maximum power from diesel engine 20 is delivered equally by motor 50 to the vehicle wheels l2, l4, l6 and 18. A characteristic for a condition less than rated load when power pedal 44 is only partially depressed may be represented by the curve designated reduced power" in FIG. 5. The load conditions such as the surface and soil characteristics of the ground over which the vehicle wheels are passing determine the speed of motor 50 corresponding to the power called for by the position of power pedal 44, as modified by other inputs to protection and regulation circuit 78.

When power pedal 44 is operated to a new position calling for less than rated power, the magnitude of the reference power" signal from protection and regulation circuit 78 is changed, thereby varying the excitation of field winding 56 and also varying the magnitude of the sine and cosine signals V, and V, and the low frequency output control signal VT, from angle sensor 64 and consequently changing the magnitude of the terminal voltage VT applied by cycloconverter 58 to armature winding 54. Electric drive 22 maintains the field winding current I, constant corresponding to such new position of power pedal 44 calling for less than rated power and regulates the sine and cosine signals V, and v, to sine and cosine winding 68 and 70 to provide a magnitude of terminal voltage VT to stator winding 36 which may be represented by the dotted curve designated reduced power" in FIG. 8.

DETAILED DESCRIPTION Synchronous Motor Synchronous motor 50 is shown schematically in FIG. 1 and in detail in FIGS. 2 and 3 and preferably is of the inductor type. The rotor 52 is coupled to hub 94 of vehicle wheel 12 through a shaft 96 and a gear box 98 containing gears 100 which provide the desired stepdown ratio between motor 50 and wheel l2.

Rotor 52 is solid and preferably of ferromagnetic material such as steel and has circumferentially spaced, chordlike portions 102 at both ends. The circumferential portions 104 between the flat portions 102 have the smallest airgaps with the motor stator and form salient rotor poles when field coil 56 is energized. Motor 50 is shown and described as a six-pole motor, and the salient pole portions 1040 at one end of rotor 52 are circumferentially displaced by 60 from the salient pole portions 104b at the other end thereof.

A plurality of axially spaced circumferential slots 106 may be provided in the salient pole portions 104 to reduce eddy current losses at high speeds and minimize heat generation. The surfaces of the rotor pole portions 104 may also be infused with silicon to increase resistivity and thus minimize eddy currents.

Motor 50 has a hollow housing formed by an annular yoke 108 closed at its open ends by end bells 110 and 112, and rotor 52 is rotatably supported within the motor housing by bearings 114 located in the end bells 110 and 112. Degaussing coils 116 supported on end bells 110 and 112 in surrounding relation to the bearings 114 generate magnetic fields which oppose the magnetic fields of stator winding 54 and field winding 56 to protect bearings 114 from overheating caused by eddy currents. The motor stator 118 is positioned on the inner periphery of yoke 108 and is formed of two axially spaced groups 120 and 122 of stator laminations each of which preferably has 36 radially inward extending teeth forming winding slots for stator winding 54. One lamination group 120 is positioned radially opposite the rotor poles 104a, while the other lamination group 122 is positioned opposite rotor poles 104b on the opposite end of rotor 52. The winding slots formed by the radial teeth in both groups of laminations 120 and 122 are in axial alignment, and a three-phase, six-pole, stator winding 54 of conventional diamond shaped configuration is positioned in the winding slots of both groups of stator laminations 120 and 122 with the coil sides extending through the aligned slots of both groups oflaminations and the coil end turns located at the ends ofstator 118.

The exciting, or field winding 56 is circumferentially wound and is located in the axial space between the two groups ofstator laminations 120 and 122 and opposite the central circular portion 124 of rotor 52. The stator laminations 120 and 122 and armature coils 54 and exciting coil 56 may be encapsulated as a unitary assembly in a suitable thermosetting resin to provide mechanical strength and environmental protection.

Exciting coil 56 is energized by electric drive 22 with direct current and generates a toroidal magnetic flux field having a magnetic flux path shown in FIG. 2 by the series of arrows and it will be noted that the flux flows through yoke 108 parallel to the axis, radially inward through stator laminations 120 and the motor airgap into pole portions 104a on one end of rotor 52, axially through rotor 52, radially outward from pole portions 104!) at the other end of rotor 52 and across the airgap and radially through stator laminations 122 and back to yoke 108. Adopting the convention that magnetic flux enters the south pole ofa magnetic body and leaves the north pole, it will be appreciated that energization of exciting coil 56 makes salient portions 104a magnetic south poles and makes salient portions l04b magnetic north poles.

Stator winding 54 is energized with three-phase alternating current by cycloconverter 58 and generates a rotating magnetic field, and rotor 52 is turned in synchronism with the rotating magnetic field by the torque resulting from interaction between the magnetic poles created on the rotor 52 by the exciting coil 56 and the rotating magnetic field.

Angle Sensor The three phase rotary inductor, vector adder, or angle sensor 64 is disclosed in the copending application of entitled "Rotary Inductor," having the same assignee as the present invention and to which reference is made for details of construction. Angle sensor 64 vectorially adds two in-phase signals V, and V, representative of the y and x rectangular coordinates of a curve of FIG. 21 and generates an output signal of a frequency which, after demodulation, is a function of the speed of motor 50 and whose magnitude and phase angle are the polar coordinates of such curve. The preferred embodiment of angle sensor 64 shown in FIGS. 14 and 9 includes a stator 72 mounted at the end of the motor housing and comprising a plurality of annular, silicon steel laminations 128 each of which has 36 radially inward extending teeth 130. One primary coil 132 (see FIG. 4) and at least one secondary coil 134 surround each tooth 130 and are inductively linked by the ferromagnetic tooth, and the permeance of the path for magnetic flux in each tooth, and thus the flux linkage between primary coil 132 and secondary coil 134 surrounding the tooth vary as the ferromagnetic angle sensor rotor 74 having three circumferentially spaced lobes 136 is rotated within stator 72 by motor 50.

Angie sensor rotor 74 may be constructed of stacked silicon steel laminations and is provided with radially inward extending portions, or valleys between the lobes 136 so that it has varying magnetic reluctance gaps, i.e., airgap spacings from teeth l36, for example the smallest airgap spacing is from teeth 4, 16 and 28 at the rotor position illustrated in FIG. 9. The magnetic fluxes induced in teeth 1-36 by primary coils 132 flow in flux paths through the teeth and across the airgap into the rotor 74 and return through the stator 72. The permeances of the paths for the magnetic fluxes generated by primary coils 132 in teeth 1-36, and thus the voltage levels of the signals induced in secondary coils 134, are functions of the position of rotor 74. Rotor 74 is preferably contoured so that the permeances of the magnetic flux paths through teeth 1 36 and across the airgaps into the rotor 74 vary sinusoidally, thereby sinusoidally varying the flux linkage between the two coils 132 and 134 inductively linked by each tooth 130 as rotor 74 rotates. The sinusoidal flux modulation produced by rotor 74 is at the frequency of rotation of motor rotor 52 and is superimposed upon a base or average flux, i.e., the base flux when subtracted from the total flux results in the pure sinusoidal flux. Such sinusoidal variation of the permeances of the magnetic flux paths over a base flux assures that the current through each primary winding 68 and 70 will be constant if the energizing voltage V, and V, is constant and further assures that the sum of the magnetic fluxes in the positive" and negative" teeth is zero at all positions of rotor 74. The magnetic flux linkage between the primary and secondary coils 132 and 134 on each tooth 130 is a maximum when a lobe 136 on rotor 74 is opposite a tooth 130 (and the airgap between rotor 74 and the tooth 130 is thus a minimum) and is a minimum when a valley between the lobes 136 is opposite a tooth 130 (and the airgap between rotor 74 and the tooth 130 is a maximum).

The eighteen odd-numbered teeth 1, 3, 5, 7, 9, etc. may be associated with the primary cosine winding 70 and are termed cosine teeth, and the eighteen even-numbered teeth 2, 4, 6, 8, 10, etc. may be associated with the primary sine winding 68 and are termed sine" teeth. Synchronous motor 50 preferably has six poles, and since angle sensor rotor 74 is directly coupled to the motor rotor 52, the angle sensor 64 preferably has three pole-pairs. It may be considered that teeth 112 constitute one pole-pair, teeth 1324 constitute a second pole-pair, and teeth 2536 constitute a third polepair.

Cosine primary winding 70 may include the serially connected primary coils 132 wound in opposite directions on successive odd-numbered teeth such as 1, 3, 5, 7, 9, etc. starting on tooth 1 so that the magnetic fluxes are generated in opposite directions in successive cosine teeth, and for convenience of description teeth 1, 5, 9, 13, 17, etc. are arbitrarily termed positive" cosine teeth and the direction of magnetic flux generated therein is shown by radially outward arrows in FIG. 9, and teeth 3, 7, 11, 15 are termed negative" cosine teeth and the direction of magnetic flux flow therein is shown by radially inward arrows. Sine winding 68 (which is displaced one-half pole pitch or electrical, i.e., 3O mechanical, degrees from cosine winding 70) may comprise the serially connected primary coils 132 wound on successive even-numbered teeth such as 4, 6 8, 10, 12, 14, etc. starting at tooth 4 so that the magnetic fluxes are generated in opposite directions in successive sine teeth, and teeth 4, 8, 12, 16, etc. 

1. An electric drive providing constant output power over a speed range and adapted to be energized from an alternating current source comprising, in combination, a synchronous electric motor having a stator winding, a rotor, and means for generating magnetic poles in said rotor, means for generating a speed signal which is a function of the speed of said motor, first function generating means responsive to said speed signal for deriving a first alternating signal in accordance with one of the rectangular coordinates of a variable parameter curve whose parameter is speed of said motor and whose radius vector and vectorial angle polar coordinates are the magnitude and phase angle of the terminal voltage to be applied to said stator winding to keep said magnetic poles on said rotor locked in with the rotating magnetic field generated by said stator winding over said speed range, second function generating means responsive to said speed signal for deriving a second alternating signal in accordance with the other rectangular coordinate of said curve, vector adder means operatively connected to said motor for vectorially adding said first and second signals and generating an output signal whose magnitude is the vector sum and whose phase angle is a function of the quotient of said first and second alternating signals and for modulating said output signal at a frequency which is a function of the speed of said motor, means for demodulating said output signal, and a frequency converter between said alternating current source and stator winding and controlled by the demodulated output signal.
 2. An electric drive in accordance with claim 1 wherein said vector adder means is a rotary inductor and has displaced first and second energizing windings coupled to said first and second function generating means respectively, an output winding inductively linked to said energizing windings and in which said output signal is induced, and rotor means operatively connected to the motor rotor for cyclically varying the flux linkage between said energizing and output windings as it rotates.
 3. An electric drive in accordance with claim 1 wherein the variable parameter of said curve has a coefficient and said motor has a plurality of said curves all of which are of the same shape but each of which has a different coefficient for said parameter and represents a different output power from said motor, and wherein the radius vector and vectorial angle polar coordinates of each of said curves are the magnitude and phase angle of the terminal voltage to be applied to said motor stator winding to keep said magnetic poles on said rotor locked in with the rotating magnEtic field generated by said stator winding over the speed range for the output power represented by said curve, and including means for selectively generating a power signal which is a function of the desired power output from said motor, wherein said first and second function generating means are also responsive to said power signal and vary said first and second alternating signals as functions of said power signal, and wherein said means for generating magnetic poles on said motor rotor includes a field winding and also including means for applying a voltage to said field winding which is a function of said power signal.
 4. An electric drive in accordance with claim 1 wherein said second function generating means includes means responsive to said speed signal for deriving a third signal which is a function of the radius vector polar coordinate of said curve, means for deriving a fourth signal which is the vector sum of said first and second alternating signals, and means for comparing said third and fourth signals, the output of said comparing means being said second alternating signal which is in accordance with said other rectangular coordinate of said curve.
 5. An electric drive in accordance with claim 4 wherein said first function generating means includes means responsive to said speed signal for deriving a first DC signal in accordance with said one rectangular coordinate of said curve, means for generating a carrier signal, and a first modulator coupled to said carrier signal generating means and to said first DC signal deriving means for varying the magnitude of said carrier signal in accordance with said first DC signal.
 6. An electric drive in accordance with claim 5 wherein said second function generating means includes means responsive to said speed signal for deriving a second DC signal which is a function of the radius vector polar coordinate of said curve, means for vectorially adding said first and second alternating signals to produce a resultant signal, means for rectifying said resultant signal, means for comparing said second DC signal with the rectified signal from said rectifying means to derive a difference signal, and a second modulator coupled to said carrier signal generating means and to said comparing means for varying the magnitude of said carrier signal in accordance with said difference signal, whereby the output from said second modulator is said second alternating signal in accordance with the other rectangular coordinate of said curve.
 7. An electric drive in accordance with claim 6 wherein said vector adder means is a rotary inductor and has first and second energizing windings in quadrature coupled to said first and second function generating means respectively, an output winding inductively linked to said energizing windings in which said output signal is induced, and ferromagnetic rotor means operatively connected to said motor rotor for modulating the flux linkage between said energizing and output windings as a function of the speed of said motor as it rotates.
 8. An electric drive in accordance with claim 7 wherein said means for vectorially adding includes means for shifting the phase of said second alternating signal 90*, and means for summing the output signal from said phase shifting means and said first alternating signal.
 9. An electric drive in accordance with claim 7 wherein said motor has a plurality of said variable parameter curves in which motor speed is the variable parameter and said parameter has a coefficient and all of said curves are of the same shape and each curve has a different coefficient for said parameter and represents a different power output from said motor, the radius vector and vectorial angle polar coordinates of each said curve being the magnitude and phase angle of the terminal voltage to be applied to said stator winding to keep said magnetic poles on said motor rotor locked in with the rotating magnetic field Generated by said stator winding over the speed range for the motor output power represented by said curve, and including means for selectively deriving a power signal which is representative of said coefficient and the desired power output from said motor; said means for deriving said first DC signal and said means for deriving said second DC signal also being responsive to said power signal.
 10. An electric drive in accordance with claim 9 wherein said means for generating magnetic poles on said motor rotor includes a field winding on the stator of said motor and including means for applying to said field winding a voltage which is a function of said power signal.
 11. An electric drive in accordance with claim 2 wherein said rotary inductor, vector adder means includes a ferromagnetic stator having radially extending teeth and said first and second energizing windings and said output winding have turns encircling said teeth and said ferromagnetic rotor means revolves within said ferromagnetic stator and cyclically modulates the permeances of the paths for the magnetic fluxes generated in said teeth by said turns of said energizing windings.
 12. An electric drive in accordance with claim 3 wherein said first and second function generating means derive first and second in-phase alternating signals which increase approximately equally as a function of said speed signal from zero motor speed up to the base speed at the lower limit of said speed range and whose magnitude is proportional to said power signal, whereby the phase angle of said output signal is substantially constant from zero motor speed to said base speed.
 13. An electric drive in accordance with claim 12 wherein said first and second function generating means derive first and second in-phase alternating signals which vary in opposite directions in accordance with said speed signal from said base speed up to a higher predetermined motor speed and which maintain said output signal constant for a selected power signal over said speed range, whereby the phase of said output signal varies as a function of motor speed from said base speed to said higher predetermined speed.
 14. An electric drive in accordance with claim 6 wherein said means for deriving a second DC signal generates a signal which varies linearly with motor speed from zero speed to said base speed and has a fixed magnitude proportional to said power signal over said motor speed range.
 15. An electric drive in accordance with claim 8 and including first switching means for selectively reversing the energization of said second energizing winding, whereby the phase of the voltage supplied by said frequency converter to said stator winding is shifted to control the direction of rotation or torque of said motor.
 16. An electric drive in accordance with claim 15 and including second switching means for selectively reversing the energization of said first energizing winding, whereby the displacement angle between said magnetic poles on said motor rotor and said magnetic field generated by said motor stator winding is changed from positive to negative and said motor is regeneratively braked when said first and second switching means are operated.
 17. An electric drive in accordance with claim 3 wherein said motor rotor is solid and ferromagnetic and has circumferentially spaced salient pole portions forming low reluctance airgaps with the motor stator and wherein said salient pole portions are also spaced axially and said field winding generates axially spaced magnetic poles of opposite polarity in said axially spaced salient pole portions.
 18. An electric drive in accordance with claim 11 wherein said rotary inductor ferromagnetic stator has first and second radially extending teeth displaced ninety electrical degrees apart surrounded respectively by turns of said first and second energizing windings and wherein serially connected turns of said output winding surround both said first and said second teeth and said ferromagneTic rotor means has a lobe and varies sinusoidally the airgap between it and said teeth as it rotates.
 19. An electric drive in accordance with claim 2 and including means for supplying a signal to one of said energizing windings at zero speed of said motor having a magnitude which is a function of said power signal and which decreases as a function of said speed signal as said motor accelerates from zero speed to the base speed at the lower limit of said speed range, whereby motor torque is available at starting.
 20. The electric drive of claim 2 wherein said source of alternating current, said motor stator winding, said demodulating means and said output winding of said rotary inductor, vector adder means are polyphase and wherein said frequency converter is a cycloconverter and includes a set of controlled rectifiers between each phase of said stator winding and said alternating current source, each said set including a pair of oppositely-poled rectifiers connected to each phase of said source, and also including firing circuit means controlled by said polyphase demodulated output signal for deriving gating signals for said controlled rectifiers.
 21. The electric drive of claim 20 wherein said firing circuit means includes means for deriving reference signals which are functions of the phase voltages of said alternating current source, means for combining said reference signals and the phase demodulated output signals to derive composite sequence signals, and means controlled by said sequence signals for deriving said gating signals for said controlled rectifiers.
 22. An electric drive in accordance with claim 20 wherein said rotary inductor output winding includes n phase output windings displaced 360/n degrees apart and said rotor means sinusoidally modulates the flux linkages between said energizing and phase output windings as it revolves, said demodulating means receive the output signals induced in said phase output windings to derive demodulated phase output signals, and including means for deriving reference signals which are functions of the phase voltages of said source, and wherein said firing circuit means includes means for superimposing said demodulated phase output signals and said reference signals to derive composite sequence signals and means controlled by said sequence signals for generating gating signals for said controlled rectifiers.
 23. An electric drive in accordance with claim 22 and including clipping circuit means between said demodulating means and said firing circuit means for limiting the amplitude of said demodulated phase output signals, whereby the voltage rating of said controlled rectifiers is reduced.
 24. An electric drive in accordance with claim 23 wherein said cycloconverter includes a reactor having a midtap between each phase of said motor stator winding and each set of controlled rectifiers and wherein the anodes of all the controlled rectifiers of each said set having one polarity are commoned and connected to one end of said reactor and the cathodes of all of the controlled rectifiers of said set having the oppositely polarity are commoned and connected to the opposite end of said reactor.
 25. An electric drive in accordance with claim 22 wherein said gating signal generating means includes a plurality of zero voltage crossing detecting means associated with each said set of controlled rectifiers and each of said zero crossing detecting means receives one of said sequence signals as an input, and a plurality of means, each of which is controlled by one of said zero voltage crossing detecting means, for deriving gating signals for one of said pair of oppositely poled rectifiers which one pair is connected to a phase of said source different than the phase from which the sequence signal input to the corresponding detecting means was derived.
 26. An electric drive in accordance with claim 25 wherein each said zero crossing detecting means provides first and second outputs when said sequence signaL crosses zero in the positive-going and negative-going directions respectively and each said means for generating gating signals for one of said pair of oppositely poled rectifiers includes first and second flip-flops coupled to said zero crossing detecting means and controlled by said first and second outputs respectively, first and second oscillators controlled by said first and second flip-flops, and means including rectifiers for coupling said first and second oscillators to the gates of said pair of oppositely controlled rectifiers respectively, whereby successive DC firing pulses are applied to the gates of said controlled rectifiers.
 27. An electric drive in accordance with claim 26 wherein all of said first flip-flops are connected as a ring counter and each said first flip-flop associated with one pair of controlled rectifiers is reset by said second output from a zero crossing detecting means associated with a different pair of oppositely poled rectifiers of said set and all of said second flip-flops are connected as a ring counter and each said second flip-flop associated with one pair of controlled rectifiers is reset by said first output from a zero crossing detecting means associated with a different pair of oppositely poled flip-flops of said set.
 28. An electric drive having selectively variable power output levels and providing constant output power over a speed range for each power level and adapted to be energized from a source of alternating current, comprising, in combination: a synchronous electric motor having a stator winding, a rotor, and a field winding for generating magnetic poles in said rotor; means for deriving a speed signal which is a function of the speed of said motor; first function generating means responsive to said speed signal for deriving a first alternating signal in accordance with one parametric equation of a variable parameter curve whose variable parameter is speed of said motor and whose polar coordinates are the magnitude and phase angle of the terminal voltage to be applied to said stator winding to keep said magnetic poles in said rotor locked in with the rotating magnetic field generated by said stator winding over the speed range, second function generating means responsive to said speed signal for deriving a second alternating signal in accordance with the other parametric equation of said curve, vector adder means operatively connected to said motor rotor for deriving an output signal whose magnitude is the vector sum and whose phase angle is a function of the quotient of said first and second alternating signals and for modulating said output signal at a frequency which is a function of the speed of said motor, and a frequency changer connected between said alternating current source and said stator winding controlled by said output signal.
 29. An electric drive in accordance with claim 28 wherein said second function generating means includes means responsive to said speed signal for deriving a third signal which is a function of the radius polar coordinate of said curve, means for deriving a fourth signal which is the vector sum of said first and second alternating signals, and means for comparing said third and fourth signals to derive said second alternating signal which is in accordance with said other parametric equation.
 30. An electric drive in accordance with claim 29 wherein said first function generating means includes means responsive to said speed signal for deriving a first DC signal in accordance with said one parametric equation, means for generating a carrier signal, and a first modulator coupled to said carrier signal generating means and to said first DC signal deriving means for varying the amplitude of said carrier signal in accordance with said first DC signal.
 31. An electric drive in accordance with claim 30 wherein said second function generating means includes means responsive to said speed signal for deriving a second DC signal which is a fuNction of the radius polar coordinate of said curve, means for vectorially adding said first and second alternating signals to produce a resultant signal, means for rectifying said resultant signal, means for comparing said second DC signal and the rectified signal from said rectifying means to derive a difference signal, and a second modulator coupled to said carrier signal generating means and to said comparing means for varying the amplitude of said carrier signal in accordance with said difference signal to derive said second alternating signal in accordance with said other parametric equation.
 32. An electric drive in accordance with claim 29 wherein said vector adder means includes a rotary inductor having angularly displaced first and second energizing windings coupled to said first and second function generating means respectively, an output winding inductively linked to said first and second energizing windings in which said output signal is induced, and ferromagnetic rotor means operatively connected to said motor rotor for cyclically varying the flux linkage between said output winding and said energizing windings as it revolves.
 33. An electric drive in accordance with claim 32 wherein said motor has a plurality of said curves each of which represents a different power output from said motor and wherein all of said curves are of the same shape and the radius vector and vectorial angle polar coordinates of each curve are the magnitude and phase angle of the terminal voltage to be applied to said stator winding to keep the output power represented by said curve constant over the speed range and including means for selectively deriving a power signal which is a function of the desired power output from said motor and wherein said first and second function generating means are also responsive to said power signal and vary the magnitude of said first and second alternating signals in accordance with said power signal, and including means for applying a voltage to said field winding which is a function of said power signal.
 34. An electric drive in accordance with claim 32 wherein said rotary inductor vector adder means includes a ferromagnetic stator having first and second teeth angularly displaced apart, said first and second energizing windings have turns which respectively surround said first and second teeth, said output winding has turns surrounding said first tooth connected in series with turns surrounding said second tooth, and said rotor means is disposed adjacent said rotary inductor stator and is rotatable relative thereto and forms a portion of the paths for magnetic fluxes generated in said teeth and cyclically varies the permeances of said magnetic flux paths as it rotates.
 35. An electric drive in accordance with claim 34 wherein said rotor means is a ferromagnetic rotor member having a lobe portion which has the smallest magnetic reluctance gap from said teeth and a dale portion having a greater magnetic reluctance gap from said teeth than said lobe portion and said rotor means sinusoidally varies the permeances of said magnetic flux paths as it rotates.
 36. An electric drive in accordance with claim 35 wherein said rotary inductor stator has a set of said first teeth angularly displaced from each other and a set of said second teeth angularly displaced from each other, said set of first teeth is angularly displaced from said set of second teeth, said first energizing winding has serially connected turns surrounding each of said first teeth and said second energizing winding has serially connected turns surrounding each of said second teeth, and said output winding has serially connected turns surrounding teeth of said first set and teeth of said second set, whereby said output signal induced in said output winding is a function of the magnitude of said first and second signals applied to said first and second energizing windings, the angle between said first and second set of teeth, and the position of said rotor member.
 37. An elEctric drive in accordance with claim 36 wherein said rotary inductor stator is annular, said first and second teeth extend radially inward, and said set of first teeth is displaced 90 electrical degrees from said set of second teeth.
 38. An electric drive in accordance with claim 37 wherein said output winding has turns surrounding a pair of said first teeth angularly displaced 180 electrical degrees apart and arranged in series opposition to cancel the base component of the magnetic flux and connected in series with turns surrounding a pair of said second teeth displaced 180 electrical degrees apart and arranged in series opposition to cancel the base component of the magnetic flux.
 39. An electric drive in accordance with claim 37 wherein said source, said motor stator winding, and said rotary inductor output winding have n phases, said first teeth are angularly displaced 60 electrical degrees apart and said second teeth are displaced 60 electrical degrees apart and positioned between said first teeth, said output winding includes n phase output windings each of which has turns surrounding a pair of said first teeth displaced 180 electrical degrees apart and arranged in series opposition connected in series with turns surrounding a pair of said second teeth displaced 180 electrical degrees apart and arranged in series opposition and wherein said turns of each said phase output winding surround teeth displaced 360/n electrical degrees from the teeth surrounded by the turns of the other phase output windings.
 40. An electric drive in accordance with claim 37 wherein said source, said motor stator winding, and said rotary inductor output winding have n phases and each rotary inductor phase output winding includes turns surrounding one of said first teeth connected in series with turns surrounding one of said second teeth and said one first tooth and said one second tooth are displaced by 360/n electrical degrees from the corresponding teeth surrounded by the turns of the other rotary inductor output phase windings.
 41. An electric drive in accordance with claim 40 wherein each rotary inductor phase output winding has turns surrounding a pair of said first teeth angularly displaced 180 electrical degrees apart and arranged in series opposition connected in series with turns surrounding a pair of said second teeth angularly displaced 180 electrical degrees apart and arranged in series opposition and said pair of first and said pair of second teeth are displaced by 360/n electrical degrees from the pairs of corresponding teeth surrounded by turns of the other rotary inductor phase output windings.
 42. An electric drive in accordance with claim 40 wherein said motor has P poles and said rotary inductor output winding has P/2 pole pairs and each rotary inductor phase output winding includes turns surrounding one of said first teeth in each pole pair connected in series with turns surrounding one of said second teeth in said pole pair and being connected in series with similarly arranged turns surrounding first and second teeth of the other pole pairs, and wherein said rotary inductor rotor means has P/2 lobes with dales between said lobes and sinusoidally varies the permeances of the magnetic flux paths through the teeth in all of said pole pairs as it rotates.
 43. An electric drive having selectively variable power output levels and providing constant output power over a speed range for each power level and adapted to be energized from a source of alternating current comprising, in combination: a synchronous electric motor having a stator winding, a rotor, and means for generating magnetic poles in said rotor; means operatively connected to said rotor for generating an output signal having a frequency which is a function of the speed of said motor; a static frequency changer connected between said source of alternating current anD said stator winding controlled by said output signal; and control means for selectively varying a condition of said output signal.
 44. The electric drive of claim 43 wherein said control means varies the phase of said output signal.
 45. The electric drive of claim 43 wherein said control means varies the magnitude of said output signal.
 46. The electric drive of claim 45 wherein said control means regulates the magnitude and shifts the phase of said output signal as functions of the speed of said motor.
 47. The electric drive of claim 46 wherein the magnitude and phase angle of the terminal voltage to be applied to said motor stator winding to keep the magnetic poles generated in said rotor locked in with the rotating magnetic field generated by said stator winding over the speed range are the radius vector and vectorial angle polar coordinates of a variable parameter curve having motor speed as the variable parameter and wherein said electric drive includes means for generating a speed signal which is a function of the speed of said motor and said control means is responsive to said speed signal and regulates the magnitude of said output signal in accordance with said radius vector and shifts the phase of said output signal in accordance with said vectorial angle over said speed range.
 48. The electric drive of claim 43 including means for selectively providing a power signal which is a function of the desired power output of said motor and wherein said control means is responsive to said power signal.
 49. The electric drive of claim 48 and including means for generating a speed signal which is a function of the speed of said motor and wherein said control means regulates a condition of said output signal as a function of the magnitude of said power signal and the magnitude of said speed signal.
 50. The electric drive of claim 48 wherein, for a given magnitude of said speed signal, said control means varies the magnitude of said output signal as a function of the magnitude of said power signal.
 51. The electric drive of claim 48 wherein, for a selected magnitude of said power signal, said control means shifts the phase of said output signal as a function of the speed of said motor.
 52. The electric drive of claim 48 wherein said electric motor also has a field winding and including means for energizing said field winding as a function of said power signal.
 53. The electric drive of claim 48 wherein said motor has a plurality of variable parametric curves of the same shape whose parameter is the speed of said motor and each of which represents a different power output from said motor and the radius vector and vectorial polar coordinates of each said curve are the magnitude and phase angle of the terminal voltage to be applied to said stator winding to keep the rotor poles generated in said motor rotor locked in with the rotating magnetic field generated by said stator field, and thus keep the motor power output constant, over the speed range and wherein said electric drive includes means for deriving a speed signal which is a function of the speed of said motor and said control means is responsive to both said speed signal and to said power signal and, for a selected power signal, regulates the magnitude of said output signal and shifts the phase of said output signal in accordance with the radius vector and vectorial angle polar coordinates of the curve corresponding to said selected power signal.
 54. The electric drive of claim 51 wherein, for said selected magnitude of power signal, said control means also maintains the magnitude of said output signal substantially constant from the base speed at the lower limit of the speed range at which constant maximum power is developed by said motor up to the upper limit of said speed range.
 55. The electric drive of claim 43 wherein said means for generating an output signal is a rotary inductor having a primary winding and a secondary winding inductively linked to said primary winding and in whiCh said output signal is induced and said control means includes said primary and secondary windings and shifts the phase and regulates the magnitude of said output signal as a function of the speed of said motor.
 56. The electric drive of claim 55 wherein said rotary inductor means for generating said output signal includes ferromagnetic rotor means operatively connected to said motor rotor for modulating the flux linkage between said primary and secondary windings as said ferromagnetic rotor means is rotated by said motor rotor.
 57. The electric drive of claim 56 wherein said rotary inductor means includes a stator, said rotor means turns within said stator, and said primary and secondary windings are on said stator.
 58. The electric drive of claim 57 wherein said rotor means has a lobe and sinusoidally varies the flux linkage between said primary and secondary windings as it rotates.
 59. The electric drive of claim 56 wherein said rotary inductor means is a vector adder and has a pair of displaced primary windings inductively linked to said secondary winding and said ferromagnetic rotor means cyclically modulates the flux linkage between each of said primary windings and said secondary winding as it rotates.
 60. The electric drive of claim 54 wherein the displacement angle between said magnetic poles on said motor rotor and the magnetic field generated by said motor stator winding varies with motor speed from the base speed at the lower limit of said speed range up to a higher predetermined speed, and wherein said control means shifts the phase of said output signal as a function of the speed of said motor from said base speed to said higher predetermined speed while maintaining the magnitude of said output signal constant.
 61. An electric drive in accordance with claim 49 wherein said alternating current source, said stator winding, and said frequency converter have n phases, said output signal generating means includes means for deriving n phase, alternating output signals modulated at a frequency which is a function of the speed of said motor, and said control means includes a demodulator receiving said phase output signals as an input to derive demodulated output signals and means for regulating the phase and magnitude of said phase output signals as functions of both said speed signal and said power signal.
 62. An electric drive in accordance with claim 43 wherein said alternating current source and said stator winding have n phases, said frequency converter is a cycloconverter and includes a set of controlled rectifiers between each phase of said stator winding and said alternating current source and each set includes a pair of oppositely poled rectifiers connected to each phase of said source, said output signal generating means includes means for deriving n phase output signals having a frequency which is a function of the speed of said motor, and said control means includes means for regulating the phase and magnitude of said phase output signals as a function of the speed of said motor and firing current means controlled by said regulated phase output signals for deriving gating signals for said controlled rectifiers.
 63. An electric drive in accordance with claim 62 wherein said output signal generating means derives n phase, alternating output signals modulated at a frequency which is a function of the speed of said motor and said control means includes discriminator means for demodulating said phase output signals, and said firing circuit means includes means for deriving reference signals which are functions of the phase voltages of said alternating current source, means for combining said reference signals and the demodulated phase output signals to derive composite sequence signals and means controlled by said sequence signals for generating said gating signals for said controlled rectifiers.
 64. An electric drive in accordance with claim 48 wherein said synchronous motor is of the inductor type and said moTor rotor is solid and ferromagnetic and said means for generating magnetic poles in said rotor includes a field winding on said motor stator and including means for energizing said field winding as a function of said power signal.
 65. An electric drive in accordance with claim 64 wherein said motor rotor has circumferentially spaced salient pole portions providing a low reluctance path to the motor stator and chordlike portions between said pole portions forming a high reluctance airgap with said motor stator and said salient pole portions are also axially spaced apart and said field winding generates axially spaced magnetic poles of opposite polarity in said axially spaced pole portions.
 66. An electric drive having selectively variable power output levels and providing constant output power over a speed range for each selected power level and adapted to be energized from a source of alternating current comprising, in combination: a synchronous electric motor having a stator winding, a rotor, and means for generating magnetic poles in said rotor; means operatively connected to said motor rotor for generating an output signal having a frequency which is a function of the speed of said motor, control means for selectively shifting the phase and regulating the magnitude of said output signal as a function of the speed of said motor; and a frequency converter connected between said source of alternating current and said stator winding controlled by said output signal.
 67. An electric drive in accordance with claim 66 wherein said means for generating an output signal is a rotary inductor having an energizing winding and a secondary winding inductively linked to said energizing winding in which said output signal is induced.
 68. An electric drive in accordance with claim 67 wherein said rotary inductor is a vector adder having displaced first and second energizing windings inductively linked to said secondary winding and said control means includes said energizing and secondary windings and vectorially adds first and second signals applied to said first and second energizing windings and induces said output signal in said secondary winding whose magnitude is equal to the vector sum of said first and second signals and whose phase is shifted relative to said first and second signals by an angle which is a function of the ratio of said first and second signals.
 69. An electric drive in accordance with claim 68 wherein said rotary inductor includes ferromagnetic rotor means operatively connected to said motor rotor for cyclically modulating the flux linkage between said secondary winding and said energizing windings as it rotates.
 70. An electric drive in accordance with claim 69 wherein said secondary winding includes first and second serially connected coils and the paths of the magnetic fluxes generated by said first and second energizing windings link said first and second coils respectively and said rotary inductor rotor means is solid and cyclically varies the permeances of said magnetic flux paths as it is revolved by said motor rotor.
 71. An electric drive in accordance with claim 70 wherein said control means includes function generating means for providing in-phase, first and second alternating signals to said first and second energizing windings which are functions of the speed of said motor.
 72. An electric drive in accordance with claim 71 wherein said function generating means provides first and second signals to said first and second energizing windings respectively which vary in the same direction as functions of the speed of said motor from zero speed up to the base speed at the lower limit of said speed range at which maximum constant power is delivered by said motor and which vary in opposite directions as functions of the speed of said motor from said base speed up to a higher predetermined speed, whereby the phase of said output signal is constant from zero speed to said base speed and is varied as a function of thE speed of said motor from said base speed to said higher predetermined speed.
 73. An electric drive in accordance with claim 72 wherein the magnitude and phase angle of the voltage to be applied by said cycloconverter to said stator winding to keep said magnetic poles generated in said motor rotor locked in with the rotating magnetic field generated by said stator winding over said speed range are the polar coordinates of a curve whose variable parameter is the speed of said motor and wherein said function generating means derive in-phase first and second signals in accordance with the x and y parametric equations of said curve.
 74. An electric drive in accordance with claim 71 wherein the displacement angle between said magnetic poles on said motor rotor and the magnetic field generated by said motor stator winding varies with motor speed along a displacement angle versus speed characteristic from the base speed at the lower limit of said speed range up to a higher predetermined speed, and wherein said function generating means provides in-phase first and second alternating signals to said first and second energizing windings which maintain the magnitude of said output signal constant and shift the phase of said output signal in accordance with said characteristic in the range from said base speed to said higher predetermined speed.
 75. An electric drive in accordance with claim 66 wherein said synchronous motor is of the inductor type and said motor rotor is solid and said means for generating magnetic poles in said motor rotor includes a field winding on the stator of said motor.
 76. An electric drive in accordance with claim 75 wherein said motor rotor is of ferromagnetic material and has circumferentially spaced salient pole portions providing a low reluctance path to the motor stator and chordlike portions between said pole portions forming a high reluctance airgap with said motor stator.
 77. An electric drive in accordance with claim 76 wherein said salient pole portions on said motor rotor are also axially spaced apart and said field winding generates axially spaced magnetic poles of opposite polarity in said axially spaced pole portions.
 78. An electric drive in accordance with claim 72 wherein said means for generating magnetic poles on said motor rotor includes a field winding, and including means for selectively deriving a power signal which is proportional to the desired power output level of said motor, means for energizing said field winding as a function of the magnitude of said power signal, and wherein said function generating means is responsive to said power signal and provides in-phase first and second alternating signals to said first and second energizing windings which are functions of both said power signal and the speed of said motor.
 79. An electric drive in accordance with claim 78 wherein said function generating means provides in-phase first and second alternating signals to said first and secondary energizing windings which vary in magnitude as a function of said power signal and which provide a fixed magnitude of said output signal over a speed range for each selected magnitude of said power signal.
 80. An electric drive in accordance with claim 79 wherein said function generating means provides first and second signals to said first and second energizing windings which vary in the same direction as functions of motor speed from zero speed up to the base speed at the lower limit of said speed range and which vary in opposite directions as functions of motor speed from said base speed up to a higher predetermined speed and shift the phase of said output signal as a function of motor speed from said base speed to said higher predetermined speed and maintain the magnitude of said output signal constant over said speed range for each selected magnitude of said power signal.
 81. An electric drive in accordance with claim 80 and including regulating means for providing a signal to one of said energizing windings whOse magnitude is a function of said power signal from zero motor speed to said base speed, whereby said output signal is induced in said secondary winding and motor torque is available at starting.
 82. An electric drive in accordance with claim 81 wherein said regulating means varies the magnitude of said signal to said one energizing winding inversely as a function of motor speed as said motor accelerates from zero speed to said base speed.
 83. An electric drive in accordance with claim 80 wherein the displacement angle between said magnetic poles on said motor rotor and the magnetic field generated by said motor stator winding varies with motor speed up to said higher predetermined speed along a displacement angle versus speed characteristic and wherein said function generating means provides alternating in-phase first and second signals to said first and second energizing windings which vary in opposite directions and shift the phase of said output signal in accordance with said characteristics from said base speed to said higher predetermined speed.
 84. An electric drive in accordance with claim 69 wherein said rotary inductor includes a stator, said energizing windings and said secondary winding are on said stator and said ferromagnetic rotor means is solid and varies the flux linkage between said secondary winding and said energizing windings as it rotates.
 85. An electric drive in accordance with claim 70 wherein said rotary inductor includes a ferromagnetic stator having displaced first and second teeth surrounded respectively by said first and second energizing windings and also surrounded respectively by said first and second coils and wherein said ferromagnetic rotor means is contoured to sinusoidally vary the gap it has with said first and second teeth as it is rotated by said motor rotor, whereby the permeances of the magnetic flux paths through said teeth and into said rotor means are varied as said rotor means revolves.
 86. An electric drive in accordance with claim 68 wherein said rotary inductor includes a ferromagnetic stator having a set of first teeth angularly displaced from each other and a set of second teeth angularly displaced from each other, said set of first teeth is angularly displaced from said set of second teeth, said first energizing winding has serially connected turns surrounding each of said first teeth, said second energizing winding has turns surrounding each of said second teeth connected in series, and said secondary winding has serially connected turns surrounding teeth of said first set and teeth of said second set, whereby said output signal induced in said secondary winding is a function of the magnitude of said first and second signals applied to said first and second energizing windings, the displacement angle between said sets of first and second teeth, and the position of said rotor means.
 87. An electric drive in accordance with claim 86 wherein said rotary inductor stator is annular, said first and second teeth extend radially inward, and said set of first teeth is displaced 90 electrical degrees from said set of second teeth.
 88. An electric drive in accordance with claim 87 wherein said alternating current source and said motor stator winding have n phases and said rotary inductor secondary winding includes n phase output windings each of which includes turns surrounding one of said first teeth connected in series with turns surrounding one of said second teeth and said one first tooth and said one second tooth are displaced by 360/n electrical degrees from the corresponding teeth surrounded by the turns of the other rotary inductor phase output windings.
 89. An electric drive in accordance with claim 88 wherein each said rotary inductor phase output winding has turns surrounding a pair of said first teeth angularly displaced 180 electrical degrees apart and arranged in series opposition to cancel the base component of the magnetic flux connected in series with turns suRrounding a pair of said second teeth angularly displaced 180 electrical degrees apart and arranged in series opposition to cancel the base component of the magnetic flux and said pair of first and said pair of second teeth are displaced by 360/n electrical degrees from the pairs of corresponding teeth surrounded by turns of the other rotary inductor phase output windings.
 90. An electric drive in accordance with claim 78 wherein said alternating current source and said motor stator winding have n phases and said rotary inductor secondary winding includes n phase output windings and said frequency converter is a cycloconverter and includes a set of controlled rectifiers between each phase of said stator winding and said alternating current source with each set including a pair of oppositely poled controlled rectifiers connected to each phase of said source, and wherein said control means includes firing circuit means controlled by the polyphase output signal from said n phase output windings of said rotary inductor for deriving gating signals for said controlled rectifiers.
 91. An electric drive in accordance with claim 90 and including means for deriving reference signals which are functions of the phase voltages of said alternating current source and wherein said firing circuit means includes means for combining said reference signals and the phase output signals from said phase output windings of said rotary inductor to derive composite sequence signals, and means controlled by said sequence signals for deriving said gating signals for said controlled rectifiers.
 92. An electric drive in accordance with claim 90 wherein said rotor means sinusoidally modulates the permeances of said magnetic flux paths, and including discriminator means for demodulating said phase output signals from said rotary inductor phase winding to derive demodulated output signals, means for generating reference signals which are functions of the phase voltages of said source, and wherein said firing circuit means includes means for superimposing said demodulated output signals and said reference signals to derive composite sequence signals, and means controlled by said sequence signals for deriving said gating signals for said controlled rectifiers.
 93. An electric drive in accordance with claim 92 and including clipping circuit means between said discriminator means and said firing circuit means for limiting the amplitude of said demodulated phase output signals, whereby the voltage rating of said controlled rectifiers may be reduced.
 94. An electric drive in accordance with claim 90 wherein said cycloconverter includes a reactor having a midtap between each phase of said motor stator winding and each set of controlled rectifiers, said motor stator phase winding being connected to said midtap, and wherein the anodes of all of the controlled rectifiers of each said set having one polarity are commoned and connected to one end of said reactor and the cathodes of all of the controlled rectifiers of said set having the opposite polarity are commoned and connected to the opposite end of said reactor.
 95. An electric drive in accordance with claim 92 wherein said gating signal deriving means includes a plurality of zero voltage crossing detecting means associated with each said set of controlled rectifiers and each of said zero crossing detecting means receives one of sequence signals as an input, and also including a plurality of means, each of which is controlled by one of said zero voltage detecting crossing means, for deriving gating signals for one of said pairs of oppositely poled controlled rectifiers which one pair is connected to a phase of said alternating current source other than the phase from which the sequence signal input to the corresponding detecting means was derived.
 96. An electric drive in accordance with claim 95 wherein each said zero crossing detecting means provides first and second outputs when said sequence signal input crosSes zero in the positive-going and negative-going directions respectively and each of said means for deriving gating signals for one of said pairs of oppositely poled controlled rectifiers includes first and second flip-flops coupled to said zero crossing detecting means and adapted to be set by said first and second outputs respectively, first and second oscillators controlled by said first and second flip-flops, and rectifier means for coupling said first and second oscillators to the gates of said pair of oppositely-poled controlled rectifiers respectively, whereby successive DC firing pulses are applied to the gates of said controlled rectifiers. 